VIENNA  Iran's newly revealed uranium enrichment plant is a heavily guarded, still-unfinished underground facility in the arid mountains near the holy city of Qom that will be able to produce nuclear fuel  or the payload for atomic warheads, Western intelligence officials and diplomats said Friday.

The revelation suggests a network of facilities, including ones with centrifuges that would enrich uranium at much higher speed and efficiency than previously known sites.

Iran's secrecy has heightened suspicions that the new site might have been meant to produce weapons-grade uranium while U.N. monitors were focused elsewhere  concentrating on known facilities to ensure that Tehran produces only low-enriched uranium that cannot be used for weapons.

Iran says its facilities are producing nuclear fuel for power plants, not for weapons.

The head of Iran's nuclear program, Ali Akbar Salehi, called the new facility "a semi-industrial plant for enriching nuclear fuel" that is not yet complete, according to the state news agency IRNA. He suggested that U.N. inspectors would be able to visit the site.

Neither Iran nor the International Atomic Energy Agency has confirmed the facility's location or size. Western diplomats and government officials with access to intelligence provided the details on the plant, speaking on condition of anonymity because they were not authorized to speak publicly on the sensitive information.

The U.S. has known of the facility's existence for several years through intelligence developed by U.S., French and British agencies, a senior White House official said.

Western intelligence locates the plant not far from Qom  one of the holiest cities in Shiite Islam, and any military strike near that city would likely provoke a backlash among Shiite Muslims across the Middle East.
U.S. intelligence believes the facility is on a military base controlled by the Revolutionary Guards, according to a document the Obama administration sent to U.S. lawmakers. It was provided to The Associated Press by an official on condition of anonymity because, though unclassified, it was deemed confidential.

A senior U.S. administration official, who demanded anonymity for discussing intelligence, described it as "a very heavily protected, very heavily disguised facility."

The military connection could undermine Iran's contention that the plant was designed for civilian purposes.

At the Group of 20 summit in Pittsburgh, President Barack Obama and the leaders of France and Britain declared that the secret nuclear facility puts new pressure on Tehran to quickly disclose all its nuclear efforts  including any moves toward weapons development  "or be held accountable."

Speaking in New York, Iranian President Mahmoud Ahmadinejad responded that his nation was keeping nothing from international inspectors and needn't "inform Mr. Obama's administration of every facility that we have." He added that Obama would regret the statement.

Iran kept the facility, located 100 miles southwest of Tehran, hidden from the IAEA until revealing it in a letter to the IAEA on Monday. That suggests it may have done so only because it wanted to go on record before being exposed.

The Iranians claim to have withdrawn from an agreement with the IAEA requiring them to notify the agency about their intent to build any new nuclear facilities and to be subject only to a six-month notification requirement. Ahmadinejad said Friday the plant was 18 months from being operational.

But the IAEA says Tehran cannot unilaterally withdraw from that bilateral agreement.

George Perkovich, an Iran expert at Washington's Carnegie Endowment for International Peace, suggested Iran must be building at least one other unreported facility, a uranium conversion plant to provide feedstuff for the newly disclosed enrichment plant. That's because the Iranians' known conversion plant, at Isfahan, is under IAEA oversight.

"Why would you have a secret enrichment plant under a mountain if you don't have a secret conversion plant?" he asked.

Mark Fitzpatrick, a senior fellow for nonproliferation at the Washington-based Institute for Science and International Security, said there has been suspicion for some time  but no concrete evidence  that Iran had been working on a second uranium conversion facility to supplement the one at Isfahan, and he agreed that if Iran had an enrichment plant, it would also need a facility to produce the gasified uranium.

Ahmadinejad sidestepped a question about whether Iran had sufficient enriched uranium to manufacture a nuclear weapon. Still, he said Tehran rejects such armaments as "inhumane."

The plant would be about the right size to enrich enough uranium to produce one or two bombs a year, but inspectors must get inside to know what is actually going on, one U.S. official said.

The intelligence assessment cited by diplomats says the site is meant to house no more than 3,000 enriching centrifuges  much less than the more than 8,000 machines at Natanz, Iran's known enrichment facility.

But the plant, which intelligence reports say is set to start operation next year, could be set up for advanced domestically developed centrifuges that enrich uranium at much higher speed and efficiency than the decades old P-1 type centrifuges acquired on the black market and in use at Natanz.

Western officials have said Natanz has already churned out enough low-enriched material to turn out weapons-grade uranium  enriched to 90 percent and beyond  for one nuclear weapon.

The senior U.S. official suggested another rationale for having a secret facility with a smaller number of high-powered centrifuges. Fewer centrifuges "cannot produce a significant quantity of low-enriched uranium," he said. "But if you want to use the facility in order to produce a small amount of weapons-grade uranium, enough for a bomb or two a year, it's the right size.

"And our information is that the Iranians began this facility with the intent that it be secret, and therefore giving them an option of producing weapons-grade uranium without the international community knowing about it."
The new plant "could be the place where they intended to break out" of their civilian program and into a weapons mode, said David Albright of the Washington-based IISS, which has closely tracked Iran for signs of any covert proliferation.

And the fact that Iran disclosed the plant's existence only a few days before it was publicly revealed suggested to Western officials that it may have done so only because it wanted to go on record before being exposed.

"The Iranians learned that the secrecy of the facility was compromised. So they came to believe that the value of the facility as a secret facility was no longer valid," the senior U.S. administration official said.

Iran has a record of nuclear secrecy, and it is blocking an IAEA inquiry based on U.S. and other intelligence that it experimented with a nuclear weapons program.

A meeting to discuss Iran's nuclear program is scheduled in Geneva for Oct. 1 with Iran and representatives of the U.S., Russia, China, Britain, France and Germany.

Iran acknowledged running a covert enrichment program only after the National Council of Resistance in Iran revealed its existence seven years ago  a development that mushroomed into a full probe of its nuclear activities and led to three sets of U.N. Security Council sanctions for its refusal to stop.

In an e-mail Friday to the AP, the dissident group said work on a tunnel and an underground facility near Qom began "in the early part of this decade," adding that a senior general of the Iranian armed forces were responsible for the tunnel project.

The U.S. considers the council to be a terrorist organization, albeit one that has provided Washington with intelligence on Iran. The European Union removed it from its terrorism list this year.

Albright said Iran would be unable to dispel suspicions about the newly disclosed plant after revealing its existence only under apparent duress.

"Iran cannot prove that it wants to use the plant for peaceful purposes now, having Western intelligence exposing them," he said.